An RC algorithm assisted optical fiber partial discharge detection system and high-speed signal interrogation method

Abstract

The application is suitable for the field of optical fiber sensing technology and power equipment detection, and provides an RC algorithm assisted optical fiber partial discharge detection system and a high-speed signal interrogation method.The system comprises a mode-locked laser, a dispersion compensation optical fiber, an erbium-doped fiber amplifier, an optical fiber coupler No.1, a single-mode optical fiber, an adjustable optical fiber delay line, an optical fiber coupler No.2, a sensing unit, a photodetector, an oscilloscope and a PC terminal.The sensing unit is a micro-nano optical fiber coupler, which comprises an input end, an output end and a ZnO composite graphene coating area.The PC terminal inquires the signal through an RC algorithm.The RC algorithm is composed of an input layer, a storage layer and an output layer.The sensing method is to map the wavelength of an ultrashort optical pulse to time, and the non-equilibrium dispersion MZI structure encodes the chirp frequency of the broadened optical pulse.The RC algorithm optimizes the data processing method, and further improves the interrogation speed by 5 times.In addition, the combination of wavelength-to-time mapping, chirp frequency encoding and the RC algorithm realizes high sensing system stability and high demodulation speed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology and power equipment detection, and particularly relates to an RC algorithm assisted optical fiber partial discharge detection system and a high-speed signal interrogation method. BACKGROUND

[0002] The application of online condition monitoring technology in power equipment mainly includes dielectric spectroscopy analysis, dissolved gas analysis, frequency response analysis, partial discharge detection and insulation resistance measurement methods. Among them, the partial discharge detection system technology based on optical fiber sensing has important development significance due to its high precision, short response time, anti-electromagnetic interference and other characteristics.

[0003] Traditional partial discharge optical fiber sensors lack accurate calibration, and in actual application, the performance of the sensor will be affected by other environmental parameters such as temperature, electromagnetic interference degree, refractive index of the environment to be measured, etc., and it is difficult to achieve high-precision spectrum demodulation and high-speed signal interrogation. The current partial discharge sensor cannot meet the demand of high-precision ultrafast demodulation.

[0004] The wavelength-to-time (WTT) mapping method of ultra-short optical pulses is used to realize the ultrafast real-time interrogation of wavelength modulated optical fiber sensors. The use of unbalanced Mach-Zehnder interferometer (MZI) in pulse chirp microwave frequency coding (CMFE) can eliminate the interference caused by random delay, and the RC algorithm is used to optimize the data processing method, and the interrogation speed is further improved. Therefore, the RC algorithm assisted optical fiber partial discharge detection system and high-speed signal interrogation method have broad development space in the field of sensing. SUMMARY

[0005] In view of the defects and improvement needs of the prior art, the present application provides an RC algorithm assisted optical fiber partial discharge detection system, which aims to realize high sensing system stability and high demodulation speed by coating ZnO composite graphene film on the surface of a micro-nano optical fiber coupler with high coupling rate and high sensitivity, combining wavelength-to-time mapping, chirp frequency coding and RC algorithm, so as to prepare an ultra-high precision ultrafast optical fiber partial discharge sensing system.

[0006] Another purpose of the present application is to provide an RC algorithm assisted optical fiber partial discharge detection high-speed signal interrogation method.

[0007] The technical scheme adopted by the first purpose of the present application is as follows:

[0008] An RC algorithm assisted optical fiber partial discharge detection system and high-speed signal interrogation method, characterized in that: the system is composed of a mode-locked laser (1), a dispersion compensation fiber (2), an erbium-doped fiber amplifier (3), a fiber coupler No. 1 (4), a single-mode fiber (5), an adjustable fiber delay line (6), a fiber coupler No. 2 (7), a sensing unit (8), a photodetector (9), an oscilloscope (10), and a PC terminal (11).

[0009] The sensing unit (8) is a micro-nano fiber coupler, composed of an input end (8-1), an output end (8-2), and a ZnO composite graphene coating area (8-3). The PC terminal (11) interrogates the signal through RC algorithm, which is composed of an input layer (11-1), a storage layer (11-2), and an output layer (11-3).

[0010] In the RC algorithm assisted optical fiber partial discharge detection system, the laser pulses provided by the mode-locked laser (1) are transmitted through the dispersion compensation fiber (2) to the erbium-doped fiber amplifier (3) for amplification. The amplified optical pulses are further equally divided into two branches by the fiber coupler No. 1 (4), with the upper branch connected to the single-mode fiber (5) and the lower branch connected to the adjustable fiber delay line (6). The two optical pulses are coupled by the fiber coupler No. 2 (7) and transmitted to the sensing unit (8) through the input end (8-1). The sensing optical signal generated by the sensing unit (8) is converted into an electrical signal by the photodetector (9) through the output end (8-2), and is time-domain sampled by the oscilloscope (10). Finally, the signal is calculated and processed by the PC terminal (11).

[0011] The RC algorithm assisted optical fiber partial discharge detection system is characterized in that: the mode-locked laser (1) outputs a femtosecond pulse optical signal with a center wavelength of 1550 nm, a 3dB spectral bandwidth of 16 nm, a pulse width of 800 fs, and a repetition frequency of 50 MHz.

[0012] The RC algorithm assisted optical fiber partial discharge detection system is characterized in that: the fiber coupler No. 1 (4), the single-mode fiber (5), the adjustable fiber delay line (6), and the fiber coupler No. 2 (7) constitute a non-balanced dispersion MZI (Mach-Zehnder interferometer) structure.

[0013] The RC algorithm assisted optical fiber partial discharge detection system, characterized in that: the sensing unit (8) is a micro-nano fiber coupler, and the total length of the waist taper area of the micro-nano fiber coupler is 42.38 mm, and the coupling waist area diameter is 3.67 microns, and high sensitivity sensing of the coupling area to the refractive index of the external environment is realized through large-scale evanescent field effect; the ZnO composite graphene coating area (8-3) is a ZnO composite graphene film coated on the surface of the coupling waist area, and the wide band gap and high exciton binding energy characteristics of ZnO have selective characteristics for ultraviolet spectrum, and the sensitive characteristics of the sensing unit (8) to the local discharge radiation ultraviolet wave band are further improved through doping graphene.

[0014] The technical scheme adopted for the second object of the application is as follows:

[0015] An RC algorithm assisted optical fiber partial discharge detection high-speed signal interrogation method, which is used for the RC algorithm assisted optical fiber partial discharge detection system, characterized in that: the ultrashort optical pulses generated by the mode-locked laser (1) pass through the dispersion compensation optical fiber (2), and the waveform in the time domain is widened, the widened optical pulses are chirp frequency coded by the unbalanced dispersion MZI structure, the generated sensing signals are loaded onto the optical pulses by the sensing unit (8), the carrier optical pulses are received by the photodetector (9) and converted into electrical signals and transmitted to the oscilloscope (10) for presentation, and finally the RC algorithm is used to inquire the signals through the PC terminal (11).

[0016] The RC algorithm assisted optical fiber partial discharge detection high-speed signal interrogation method, characterized in that: the wavelength is mapped to the time through the mode-locked laser (1) and the dispersion compensation optical fiber (2), and the wavelength interrogation speed and resolution are respectively improved to 100 kHz and 0.2 pm by using the photonic time stretching method.

[0017] The RC algorithm assisted optical fiber partial discharge detection high-speed signal interrogation method, characterized in that: the chirp frequency coding is realized by the unbalanced dispersion MZI structure, specifically, the adjustable optical fiber delay line (6) is adjusted to keep the time domain consistent at the input end of the optical fiber coupler No. 2 (7) of the upper and lower branches of the MZI, at this time, the optical pulses load the chirp frequency information due to the total dispersion difference of the single-mode optical fiber (5) in the MZI, the chirp rate of the chirp microwave signal can be changed by adjusting the length of the single-mode optical fiber (5), and the center frequency position of the chirp signal is affected by the delay modulation of the two light paths of the MZI, and the chirp frequency coding eliminates the instantaneous microwave frequency affected by the random time shift.

[0018] The RC algorithm assisted optical fiber partial discharge detection high-speed signal inquiry method is characterized in that: the pulse frequency inquiry method using the RC algorithm in the PC terminal (11) uses a randomly generated sparse connection internal weight matrix to obtain a neuron library, an input signal is input from an input layer (11-1), is calculated by an activation function, and is transmitted to a storage layer (11-2), the storage layer (11-2) constitutes a nonlinear dynamic system, the internal states of which are periodically connected with each other, and an output signal is only composed of a linear combination of weighted internal variables, the storage layer (11-2) further transmits the signal to an output layer (11-3), a feedback matrix transmits the output signal from the output layer (11-3) to the storage layer (11-2), and finally, the output layer (11-3) outputs an optimal solution, and the RC algorithm increases the signal processing speed by 5 times.

[0019] Overall, compared with the prior art, the RC algorithm assisted optical fiber partial discharge detection system and high-speed signal inquiry method have the following beneficial effects:

[0020] 1. The micro-nano fiber coupler coupled with the ZnO composite graphene film on the surface of the waist region has high sensitivity, high selectivity and high stability, and provides high ultraviolet detection sensitivity for the system.

[0021] 2. The photon time stretching method improves the speed and resolution of the wavelength demodulation technology, and further based on the non-ambiguous dynamic wavelength detection method of the chirp microwave frequency coding, the demodulation deviation caused by the environmental random time delay is effectively solved, and the wavelength is inquired quickly and accurately in a complex situation.

[0022] 3. The RC algorithm increases the frequency evaluation speed by 5 times, and has great application advantages in the field of dynamic signal demodulation. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a principle diagram of the RC algorithm assisted optical fiber partial discharge detection system of the embodiment of the application.

[0024] Figure 2 It is a structure diagram of the sensing unit of the embodiment of the application.

[0025] Figure 3 It is a structure diagram of the RC algorithm of the embodiment of the application.

[0026] Figure 4 The frequency response of the pulse of the measurement sensor at different center wavelengths is measured.

[0027] Figure 5 The RC result of the sensing pulse with the center wavelength between 1546nm and 1550nm.

[0028] In the diagram: 1—Mode-locked laser, 2—Dispersion compensation fiber, 3—Erbium-doped fiber amplifier, 4—Fiber coupler 1, 5—Single-mode fiber, 6—Adjustable fiber delay line, 7—Fiber coupler 2, 8—Sensing unit, 8-1—Input end, 8-2—Output end, 8-3—ZnO composite graphene coating area, 9—Photodetector, 10—Oscilloscope, 11—PC terminal, 11-1—Input layer, 11-2—Storage layer, 11-3—Output layer. Detailed Implementation

[0029] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. However, the embodiments and protection scope of the present invention are not limited thereto. Any modifications that are substantially the same as those of the present invention are within the protection scope of the present invention.

[0030] like Figure 1 As shown, this invention provides an RC algorithm-assisted fiber optic partial discharge detection system, which includes a mode-locked laser (1), a dispersion-compensating fiber (2), an erbium-doped fiber amplifier (3), a fiber coupler (4), a single-mode fiber (5), an adjustable fiber delay line (6), a fiber coupler (7), a sensing unit (8), a photodetector (9), an oscilloscope (10), and a PC terminal (11).

[0031] The structure of the sensing unit (8) is as follows: Figure 2 As shown, the structure includes: an input end (8-1), an output end (8-2), and a ZnO composite graphene coating region (8-3). The composite graphene coating region (8-3) serves as the main sensing element. The sensing unit (8) is made of two standard single-mode optical fibers with some coating removed, which are cross-fused and tapered. The total length of the waist cone region of the micro-nano fiber coupler is 42.38 mm, and the diameter of the coupling waist region is 3.67 μm. High sensitivity sensing of the refractive index of the external environment is achieved through a large proportion of evanescent field. The ZnO composite graphene film covering the surface of the coupling waist region has selective characteristics for the ultraviolet spectrum due to the wide bandgap and high exciton binding energy of ZnO. The sensitivity of the sensing unit (8) to the ultraviolet light band of partial discharge radiation is further enhanced by doping with graphene. The RC algorithm structure is as follows. Figure 3 As shown, it consists of an input layer (11-1), a storage layer (11-2), and an output layer (11-3).

[0032] Furthermore, fiber coupler 1 (4), single-mode fiber (5), adjustable fiber delay line (6), and fiber coupler 2 (7) are connected in sequence to form an unbalanced dispersion MZI (Mach-Zehnder interferometer) structure.

[0033] In the embodiment, the mode-locked laser (1) outputs femtosecond pulse optical signals with a center wavelength of 1550 nm, a 3dB spectral bandwidth of 16 nm, a pulse width of 800 fs, and a repetition frequency of 50 MHz, which matches the detected spectral band.

[0034] The RC algorithm-assisted optical fiber local fault detection high-speed signal interrogation method is described below.

[0035] The ultrashort optical pulses generated by the mode-locked laser (1) pass through the dispersion compensation optical fiber (2), which widens the waveform in the time domain. The non-balance dispersion MZI structure encodes the chirp frequency of the widened optical pulses. The sensing unit (8) loads the generated sensing signal onto the optical pulses. The photodetector (9) receives the carrier optical pulses and converts them into electrical signals, which are transmitted to the oscilloscope (10) for presentation. Finally, the PC terminal (11) interrogates the signal through the RC algorithm.

[0036] Further, the chirp frequency encoding is realized by the non-balance dispersion MZI structure. Specifically, the adjustable optical fiber delay line (6) is adjusted to keep the time domain consistent at the input end of the optical fiber coupler No. 2 (7) of the MZI. At this time, the optical pulses load the chirp frequency information due to the total dispersion difference of the single-mode optical fiber (5) in the MZI. Changing the chirp rate of the chirp microwave signal can be realized by adjusting the length of the single-mode optical fiber (5). The center frequency position of the chirp signal is affected by the delay modulation of the two light paths of the MZI. The chirp frequency encoding eliminates the instantaneous microwave frequency affected by the random time shift.

[0037] Further, the RC algorithm structure is as shown in Figure 3 which is composed of an input layer (11-1), a storage layer (11-2), and an output layer (11-3).

[0038] Further, the input signal enters the input layer (11-1), and the signal is transmitted to the storage layer (11-2) after calculation by the activation function. The storage layer (11-2) constitutes a nonlinear dynamic system, in which the internal states are periodically connected to each other. The output signal is only composed of the linear combination of weighted internal variables. The storage layer (11-2) transmits the processed signal to the output layer (11-3). The feedback matrix transmits the output signal from the output layer (11-3) to the storage layer (11-2). Finally, the output layer (11-3) outputs the optimal solution.

[0039] Working principle:

[0040] Working process: the laser pulse provided by the mode-locked laser (1) is transmitted to the erbium-doped fiber amplifier (3) through the dispersion compensation fiber (2) for amplification, the amplified light pulse is further divided into two branches by the fiber coupler No. 1 (4) in equal proportion, the upper branch is connected with the single-mode fiber (5), and the lower branch is connected with the adjustable optical fiber delay line (6), then the two light pulses are coupled by the fiber coupler No. 2 (7) and transmitted to the sensing unit (8) through the input end (8-1), the sensing light signal generated by the sensing unit (8) is converted into an electric signal by the photodetector (9) through the output end (8-2), the time domain sampling is carried out by the oscilloscope (10), and finally the signal is calculated and processed by the PC terminal (11).

[0041] Measurement principle: the photon time stretching system constructed based on the real-time Fourier transform principle is used to realize stable demodulation of the signal.

[0042] The micro-nano fiber coupler utilizes the strong evanescent field effect, so that the coupling coefficient is closely related to the wavelength and the environmental refractive index, and high-precision refractive index detection is realized.

[0043] P out =P in sin 2 (CZ) (1)

[0044] Wherein Z is the coupling length of the MFC, C is the coupling coefficient of the coupling region, which can be expressed as:

[0045]

[0046] Wherein V is the normalized frequency, λ is the wavelength of incident light, a is the fiber radius of the waist region, n1 and n2 are the refractive indexes of the cladding and the environment respectively. Under the action of ultraviolet radiation, ZnO material efficiently absorbs light energy, promotes the rapid increase of electron-hole pairs, significantly changes the refractive index of ZnO, further causes the change of the coupling coefficient, leads to the drift of the transmission spectrum, and thus high-sensitivity ultraviolet detection can be realized.

[0047] The RC algorithm includes an input layer (11-1), a storage layer (11-2) and an output layer (11-3), uses a randomly generated sparse connection internal weight matrix to obtain a neuron bank to project the input into a high-dimensional nonlinear representation. The typical reservoir update equation can be described by formula (3) and formula (4):

[0048]

[0049] The storage layer (11-2) constitutes a nonlinear dynamic system, the internal states of which are periodically connected to each other, but the output is only composed of a linear combination of internal variables weighted according to formula (5). This unique feature makes the RC algorithm significantly efficient in complex time-varying classification tasks.

[0050] y(n) = W out x(n) (5)

[0051] Firstly, the frequency of the whole chirp signal was calculated using the short-time Fourier transform (STFT) method. The frequency results of the pulse signal with the center wavelength in the range of 1546 nm to 1550 nm (with a step of 1 nm) were evaluated using the RC algorithm. It was found that the frequency obtained by the RC algorithm was consistent with that obtained by the STFT method, and the linear response R 2 reached 0.979. For 100,000 sampling points, the frequency evaluation time of the RC algorithm was about 0.28 seconds, while the average time of the STFT method under the same calculation condition was about 1.42 seconds. Therefore, the RC showed higher efficiency, and the frequency evaluation speed was increased by 5 times.

Claims

1. An RC algorithm-assisted optical fiber partial discharge detection system, characterized in that: The system consists of a mode-locked laser (1), a dispersion-compensating fiber (2), an erbium-doped fiber amplifier (3), a fiber coupler (4), a single-mode fiber (5), an adjustable fiber delay line (6), a fiber coupler (7), a sensing unit (8), a photodetector (9), an oscilloscope (10), and a PC terminal (11). The sensing unit (8) is a micro-nano fiber coupler, consisting of an input end (8-1), an output end (8-2), and a ZnO composite graphene coating region (8-3); the PC terminal (11) queries the signal through the RC algorithm, which consists of an input layer (11-1), a storage layer (11-2), and an output layer (11-3). It uses a randomly generated sparse connection internal weight matrix to obtain the neuron library, so as to project the input into a high-dimensional nonlinear representation. The typical library update equation can be described by equations (1) and (2); the storage layer (11-2) constitutes a nonlinear dynamic system, whose internal states are periodically interconnected, and the output consists of a linear combination of internal variables weighted by equation (3); y(n)=W out x(n) (3) In the RC algorithm-assisted fiber optic partial discharge detection system, the laser pulse provided by the mode-locked laser (1) is transmitted through the dispersion compensation fiber (2) to the erbium-doped fiber amplifier (3) for amplification. The amplified optical pulse is further divided into two branches by fiber coupler 1 (4) in equal proportion. The upper branch is connected to the single-mode fiber (5) and the lower branch is connected to the adjustable fiber delay line (6). The two optical pulses are then coupled by fiber coupler 2 (7) and transmitted to the sensing unit (8) through the input end (8-1). The sensing optical signal generated by the sensing unit (8) is converted into an electrical signal by the photodetector (9) through the output end (8-2). The signal is then sampled in the time domain by the oscilloscope (10) and finally processed by the PC terminal (11).

2. The RC algorithm-assisted fiber optic partial discharge detection system according to claim 1, characterized in that: The mode-locked laser (1) outputs a femtosecond pulse optical signal with a center wavelength of 1550nm, a 3dB spectral bandwidth of 16nm, a pulse width of 800fs, and a repetition frequency of 50MHz.

3. The RC algorithm-assisted fiber optic partial discharge detection system according to claim 1, characterized in that: The fiber coupler No. 1 (4), single-mode fiber (5), adjustable fiber delay line (6), and fiber coupler No. 2 (7) constitute an unbalanced dispersion MZI (Mach-Zehnder interferometer) structure.

4. The RC algorithm-assisted fiber optic partial discharge detection system according to claim 1, characterized in that: The sensing unit (8) is a micro-nano fiber coupler, and the total length of the waist cone region of the micro-nano fiber coupler is 42.38 mm, and the diameter of the coupling waist region is 3.67 μm. The coupling region achieves high sensitivity sensing of the refractive index of the external environment through the large proportion of evanescent field. The ZnO composite graphene coating region (8-3) is a ZnO composite graphene film coated on the surface of the coupling waist region. The wide bandgap and high exciton binding energy characteristics of ZnO have selective characteristics for the ultraviolet spectrum. By doping graphene, the sensitivity of the sensing unit (8) to the ultraviolet light band of partial discharge radiation is further improved.

5. A high-speed signal interrogation method for fiber optic partial discharge detection assisted by an RC algorithm, the method being used in the fiber optic partial discharge detection system assisted by an RC algorithm according to claim 1, characterized in that: The ultrashort optical pulse generated by the mode-locked laser (1) is broadened in the time domain by passing through the dispersion compensation fiber (2). The unbalanced dispersion MZI structure performs chirped frequency encoding on the broadened optical pulse. The sensing unit (8) then loads the generated sensing signal onto the optical pulse. The photodetector (9) receives the carrier optical pulse and converts it into an electrical signal, which is then transmitted to the oscilloscope (10) for display. Finally, the signal is queried by the PC terminal (11) through the RC algorithm.

6. The RC algorithm-assisted high-speed signal interrogation method for fiber optic partial discharge detection according to claim 5, characterized in that: By using a mode-locked laser (1) and a dispersion-compensating fiber (2), wavelength is mapped onto time, and the wavelength interrogation speed and resolution are improved to 100 kHz and 0.2 pm, respectively, using this photonic time stretching method.

7. The RC algorithm-assisted high-speed signal interrogation method for fiber optic partial discharge detection according to claim 5, characterized in that: The chirped frequency encoding is implemented by an unbalanced dispersion MZI structure. Specifically, the adjustable fiber delay line (6) is adjusted to keep the upper and lower branches of the MZI consistent in the time domain at the input end of the second fiber coupler (7). At this time, the optical pulse is loaded with chirped frequency information due to the total dispersion difference caused by the single-mode fiber (5) in the MZI. The chirped rate of the chirped microwave signal can be changed by adjusting the length of the single-mode fiber (5). The center frequency position of the chirped signal is affected by the delay modulation of the two optical paths of the MZI. The chirped frequency encoding eliminates the instantaneous microwave frequency affected by random time shift.

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